Progressive power lenses are used for spectacle lenses having a distance vision part and a near vision part (see, for example, Patent Literature 1 to Patent Literature 7). Examples of the progressive power lenses include a front-surface progressive lens, a back-surface progressive lens, and a double-surface progressive lens. In general, a front-surface progressive lens is a lens in which an eyeball-side surface is designed as a spherical surface and an object-side surface is designed as a progressive surface. A back-surface progressive lens is a lens in which an object-side surface is designed as a spherical surface and an eyeball-side surface is designed as a progressive surface. A double-surface progressive lens is a lens in which an object-side surface and an eyeball-side surface are each designed as a progressive surface. For wearers with astigmatism prescription, these lenses each have the function of astigmatism correction by combining a cylindrical surface or a toric surface with the eyeball-side spherical surface or progressive surface.
In general, such spectacle lenses are manufactured with use of a semi-finished lens. For a back-surface progressive lens, for example, a semi-finished lens has an object-side spherical surface having a given curve value that is fixed in a predetermined power range (base curve section). For a front-surface progressive lens or a double-surface progressive lens, a semi-finished lens has an object-side surface obtained by combining a spherical surface having a given curve value with a progressive surface having a given addition in a predetermined power range. In any case, the object-side surface is a reference surface that is not processed any more. With reference to the object-side surface, the eyeball-side surface to be processed is calculated and processed in accordance with a prescription (such as distance vision power, near vision power, astigmatic power, and prism) of the wearer. The eyeball-side surface to be processed (correction surface) is a simple surface obtained by combining a progressive surface with a toric surface in some cases and is a complicated surface calculated in consideration of correction such as suppression of astigmatism in other cases. Such a correction surface can now be processed by the advanced freeforming technology.